Windows Server 2003 with SP1 includes backup APIs which can be used to determine the backup status of each Naming Context in Active Directory. The backup status is stored in the DSA Signature attribute of each Partition or Naming Context. You can query the status of backup by running the following command:
Repadmin.exe /showbackup
The above command will list the backup status of each NC. This includes the time and date when the backup was taken with NC Name. The command will list all the NCs in the Active Directory Forest including Application Partitions. This is very useful when you need to determine the backup status of each NC.